The present invention relates to a communication route guidance system for guiding a mobile unit to a destination and, more particularly, to a communication route guidance system which enables communication between a remote information center and at least one mobile unit, both storing road data. The mobile unit is equipped with a communication terminal.
Japanese patent laid-open publication No.10-19588 discloses an example of the prior art communication route guidance system wherein map image data, recommended route data (or optimum route data) and other data necessary in route guidance is transmitted from a remote information center to a mobile unit. In this system, the information center operates, in response to a request from the mobile unit, to read out necessary data from a database and to prepare the map image data. The remote information center also conducts a route search operation to prepare the optimum route data. The information center then transmits the map image data and the optimum route data thus prepared to the mobile unit. The mobile unit guides the user of the mobile unit to the destination in accordance with such data transmitted from the information center.
In some cases, however, the mobile unit is not capable of receiving data from the information center when the mobile unit is in an area where little or no such communication is available. Such an area is hereinafter referred to as a xe2x80x9cnon-communicationxe2x80x9d area. There will also be occasions when such communication will not be available because of problems or breakdown at the remote information center.
Accordingly, it is a primary object of the present invention to provide a novel communication route guidance system which is capable of guiding a mobile unit to a destination even when the mobile unit is unable to communicate with the information center, e.g. when the mobile unit is in a non-communication area or the system in the information center has broken down.
To achieve the above object, in accordance with a first aspect of the present invention, there is provided a communication route guidance system wherein an information center transmits route information to a mobile unit for guiding the mobile unit from its current position to a destination, in response to a request from the mobile unit, wherein the information center includes: first communication means for transmitting and receiving data to and from said mobile unit; first memory means for storing first road data; and first route search means for searching the first road date to obtain first route guidance data for guiding the mobile unit from its current position to the destination in accordance with information transmitted from the mobile unit through the first communication means and identifying the current position and a destination, responsive to a request from the mobile unit for a route search. The information center is further provided with data dividing means for dividing said first route guidance data into a plurality of data segments, each data segment being usable in said mobile unit as an independent item of route information providing guidance from a near end of a route segment (corresponding to the data segment) to the opposite, remote end of the route segment. The mobile unit, in turn, includes: second communication means for transmitting and receiving data to and from the information center; second memory means for storing second road data; second route search means for conducting a route search of the second road data to obtain second route guidance data for guiding the mobile unit from the current position to the destination; third memory means for storing at least one of the data segments transmitted from the information center through said first and second communication means; sensor means for detecting whether data is communicable with said information center through said first and second communication means; and route guidance means for guiding the mobile unit to the destination in accordance with at least one of said second route guidance data and said at least one data segment stored in the third memory means, the route guidance means guiding the mobile unit to the destination in accordance with the second route guidance data when the sensor means detects inability to communicate between the mobile unit and the information center.
As used herein, xe2x80x9csegmental dataxe2x80x9d has reference to a series of the data segments described above.
In a preferred embodiment of the first aspect of the present invention described above, the information center further includes information collection means for obtaining the latest traffic and road information, the first road data stored in the first memory means being updated in response to the latest traffic and road information obtained by the information collection means.
In another preferred embodiment of the first aspect of the present invention, when the mobile unit has been guided by the second route guidance data obtained by the second route search means and the sensor means has detected that data communication is available with said information center, the first route search means searches for a new optimum route to obtain new route guidance data for guiding the mobile unit from its current position to the destination in response to a request from the mobile unit, the new route guidance data being divided by said data dividing means into a plurality of said data segments which are transmitted to the mobile unit for storage in the third memory means. In this embodiment, the sensor means may comprise measurement means for measuring field intensity of a radio wave in data transmission from the information center and means for judging that data can not be communicated between the mobile unit and the information center when the measured field intensity is below a predetermined threshold level. Alternatively, the sensor means may comprise means for judging that data can not be communicated when the mobile unit receives no data segment from the information center within a predetermined time period after transmitting a request to the information center. The sensor means may also comprise communication area data memory means for storing data specifying communication areas in which the mobile unit can be in communication with the information center; and means for judging, in accordance with that data stored in the communication area data memory means, that no data communication is available between the mobile unit and the information center when the mobile unit is not within any of the specified communication areas.
In accordance with a second aspect of the present invention, there is provided a communication route guidance system wherein an information center transmits route information to a mobile unit for guiding the mobile unit from its current position to a destination, in response to a request from said mobile unit, wherein the information center includes: first communication means for receiving current position and destination from the mobile unit and transmitting data segments to the mobile unit; first memory means for storing road data; route search means for searching the stored road data to obtain route guidance data for guiding the mobile unit from its current position to the destination; data dividing means for dividing the thus obtained route guidance data into a plurality of data segments, each data segment being usable in said mobile unit as an item of route information providing guidance from a near end of a route segment (corresponding to the data segment) to the opposite, remote end of the route segment; communication area data memory means for storing data specifying communication areas wherin the mobile unit can communicate with the information center through the first communication means; and transmission route length determining means for determining number of data segments in a continuous series of data segments to be transmitted to the mobile unit while travelling within one of the specified communication areas, and for locating the extreme ends of that continuous series of data segments data within the one communication area, i.e. a near end and a far end. In this second aspect of the present invention the mobile unit includes second communication means for transmitting the current position and destination to the information center and for receiving the segmental data from the information center, second memory means for storing the received segmental data, and route guidance means for guiding said mobile unit to said destination in accordance with the segmental data stored in the second memory means.
In a preferred embodiment of the second aspect of the present invention, the information center further includes information collection means for obtaining the latest traffic and road information, the road data stored in the first memory means being updated in response to the latest traffic and road information obtained by the information collection means.
In another preferred embodiment of the second aspect of the present invention the mobile unit transmits a request to the information center for guidance to the destination, each time when a length of the remaining route for which guidance is provided by the continuous series of said segmental data which the mobile unit has last received from the information center becomes shorter than a predetermined distance, and the route search means plans said route guidance data each time the information center receives a request from the mobile unit.
In still another preferred embodiment of the second aspect of the present invention, the mobile unit transmits the requests to the information center at a predetermined periodic time interval or a predetermined increment of distance travelled by the mobile unit, and the route search means obtains route guidance data for guiding the mobile unit to the destination responsive to each of the requests.
In still another preferred embodiment of the second aspect of the present invention the route search means plans the route guidance data for guiding the mobile unit from its current position to the destination at a predetermined periodic interval in time or at a predetermined increment of distance travelled by the mobile unit.
In accordance with a third aspect of the present invention, there is provided a communication route guidance system wherein an information center transmits route information to a mobile unit for guiding the mobile unit from its current position to a destination, in response to a request from the mobile unit, wherein the information center includes: first communication means for transmitting and receiving data to and from said mobile unit; first memory means for storing first road data; first route search means for ksearching the first road data to obtain first route guidance data for guiding the mobile unit from its current position to the destination, the current position and the destination being transmitted from the mobile unit through the first communication means; and data dividing means for dividing the first route guidance data into a plurality of data segments, each data segment being usable in said mobile unit as an independent item of route information for guiding the mobile unit from one extreme end of a route segment (corresponding to the data segment) to the other end thereof. In this third aspect of the present invention the mobile unit includes second communication means for transmitting and receiving data to and from said information center; second memory means for storing second road data; second route search means for searching the stored second road data to obtain second route guidance data for guiding the mobile unit from its current position to the destination; third memory means for storing at least one of the data segments transmitted from the information center through the first and second communication means; route guidance means for guiding the mobile unit to the destination along a guide route defined by at least one segment of the second route guidance data obtained by the second route search means and the at least one data segment stored in said third memory means; first sensor means for detecting whether data can be communicated with the information center through the first and second communication means; and second sensor means for detecting that the mobile unit has strayed from the guide route; wherein the second route search means is responsive to both detection by the second sensor means that the mobile unit has strayed from the guide route and detection by the first sensor means that data cannot be communicated between the mobile unit and the information center to plan restoration route guidance data for guiding and returning the mobile unit to the guide route along which it had been guided by the route guidance means before departure therefrom detected by the second sensor means.
In a preferred embodiment of the third aspect of the present invention, the information center further includes information collection means for obtaining the latest traffic and road information, the first road data stored in said first memory means being updated in response to said latest traffic and road information obtained by the information collection means.
In another preferred embodiment of the third aspect of the present invention, the mobile unit transmits a request to the information center for guidance to the destination, each time the length of the guide route remaining guidable by the last continuous series of said segmental data received by transmission from the information center becomes shorter than a predetermined distance, and the first route search means obtains first guidance data each time the information center receives a request for guidance from the mobile unit.
In still another embodiment of the third aspect of the present invention, the mobile unit transmits requests to the information center at a predetermined periodic interval of time or at a predetermined increment of distance travelled by the mobile unit. and the first route search means plans first route guidance data for guiding the mobile unit from its current position to the destination each time the information center receives a request from the mobile unit.
In still another embodiment of the third aspect of the present invention, the first route search means obtains (plans) the first route guidance data for guiding the mobile unit from its current position to the destination at a predetermined increment of distance travelled by the mobile unit.
In accordance with a fourth aspect of the present invention, there is provided a communication route guidance system wherein an information center transmits route information to a mobile unit for guiding the mobile unit from its current position to a destination, in response to a request from said mobile unit, wherein the information center includes: first memory means for storing first location data for identifying a location by designation of at least one of the telephone number and address thereof; and first route search means for obtaining (planning) first route guidance data, for guiding the mobile unit from its current position to the destination, by reference to the first location data stored in the first memory means. In this fourth aspect the mobile unit includes: input means for inputting at least one of the telephone number and address of the destination, as destination information; communication means for transmitting the current position and the destination information to the information center and for receiving route guidance data from the information center; second memory means for storing second location data capable of specifying a location in accordance with the destination information; sensor means for detecting whether data communication with the information center is available through the communication means; second route search means for obtaining (planning) second route guidance data for guiding the mobile unit from its current position to the destination by searching the second location data stored in the second memory means, when the sensor means detects that said information input by the input means cannot be transmitted to the information center; and route guidance means for guiding the mobile unit to the destination in accordance with at least one of said first and second route guidance data.
In a preferred embodiment of the fourth aspect of the present invention, when the mobile unit has been guided by the second route guidance data obtained by the second route search means and when the sensor means has detected that data communication with the information center has become available, in response to a request from the mobile unit, the first route search means obtains new route guidance data for guiding the mobile unit from its current position to the destination, whereby the route guidance means guides the mobile unit in accordance with the new route guidance data.
In another preferred embodiment of the fourth aspect of the present invention, the second location data stored in the second memory means contains data specifying a representative location within an area including a location to be designated by input of telephone number and/or address through the input means.
In still another preferred embodiment of the fourth aspect of the present invention, the sensor means includes measurement means for measuring field intensity of a radio wave in data transmission from the information center and means for judging that data cannot be communicated with the information center when the measured field intensity is below a threshold level.
In still another preferred embodiment of the fourth aspect of the present invention the sensor means comprises means for judging that data cannot be communicated with the information center when the mobile unit receives no first route guidance data from the information center within a predetermined time period after transmitting a request to the information center.
In still another preferred embodiment of the fourth aspect of the present invention the sensor means comprises communication area memory means for storing data specifying, as communication areas, areas in which the mobile unit can communicate with the information center: and means for judging, in accordance with data stored in the communication area memory means, that there can be no communication between the mobile unit and the information center when the mobile unit is not within any of the communication areas.
Typical examples of the mobile unit mentioned above include, not only a vehicle in which navigation apparatus is mounted and a hand-held navigation apparatus for use by a pedestrian. but also personal computers, laptop computers, personal digital assistant (PDA), cellular phones, and pagers. However, in the description of the preferred embodiments which follows, in the interest of brevity, description of the mobile unit will be limited to a vehicle in which a navigation apparatus is mounted.